Wave guide joint



March 3, 1953 A. c. BECK ET A1. 2,630,489

WAVE GUIDE: JOINT Filed Nov. 6, 1945 A.C.BECK /NL/ENTORS HTFR/,S

j @5k/MA AT ZOR/VEV Patented Mar. 3, 1953 UNITED STATES PATENT OFFICE WAVE GUIDE JoiN'r poration of New York Application November 6, 1945, Serial No. 627,066

11 Claims.

This invention relates to wave guides', and more particularly to longitudinally adjustable joints in wave guides.

Joints of the kind in question may be used for a variety of purposes. As one example of useful application it may be pointed out that long wave guides are usually made of copper, brass or other conductive material having a relatively large co eiiicient of expansion. Joints of the present type may be used as an expansion joint in a wave guide or wave guide system. `Numerous other applications may arise wherein it is desired to increase or decrease the effective or total length of a wave guide during use of the same forelectrical transmission or without disturbing the'transmission. The separate sections of theguide in the case of an expansion joint may move relatively to one another as a result of temperature changes expanding or contracting the parts. However, for other applications, parts of the Vguide may be operated with respect to one another by hand or by power-driven devices. In some cases the total movement may be quite considerable, up to several inches or several feet, in comparison with the relatively smaller movement necessary in an expansion joint.

In a typical and exemplary embodiment ofthe invention the `joint consists' of an external wave guide member into which a smaller member of lesser diameter extends for vvhatever distance is necessary under the `particular circumstances of use. It has been found that electrical problems arise in connection with such an arrangement. It is not sufcient merely'that one guide or pipe be slid into another in which it fits rather tightly. Even with tight-tting members, `a considerable energy loss occurs as aA result of the electromagnetic wave energy leaking out of the crack ben tween the two members. Furthermore, inasmuch as wave guides are required to possess substantial mechanical strength, the vthickness of the pipes or tubes constituting them A'must oftentimes be quite considerable. This results in va change of diameter at the transition between the large guide member and the small guide member which results in energy reflections and, moreover, because these energy reflections vary in distance from a wave energyA source or a wave energy absorber placed along the guide, variations of impedance will appear atl-the source or at the absorber.

Consequently, `an object of theinvention is to provide an arrangement which eliminates or minimizes the diiculties inherent -in longitudinally sliding joints in wave/guides.'

In the exemplary embodiment of the invention illustrated in the accompanying drawings:

Fig. 1 is a perspective view of a wave guide joint with the outer guide member broken away to show the structure at the end of the inner guide member which structure largely embodies and exemplifies features of the invention; and

Fig. 2 is a cross-sectional View taken laterally through the central portion of the end of the inner wave guide member.

In the drawings the outer guide member l may be assumed to be terminated at a point 2 but to extend indenitely to the left. The inner guide member t has an end slidably mounted in the outer guide member i, and the inner guide member in turn extends indeiinitely to the right. The inner guide member comprises several features of construction which will now be discussed.

This particular guide as illustrated is a rectangular guide and may be assumed to transmit waves of the TE1,o type, sometimes designated the dominant wave. In such waves the lines of electric force are generally transverse as indicated by the arrow Il.

in an arrangement in which one hollow pipe is merely fitted into another, it will be found that electromagnetic power leaks out through the crack between the guide members and out into space beyond the waveguides. Not only is this loss of power undesirable but in the case of high power equipment theelectric energy escaping from the guide may set up serious disturbances in the neighborhood when picked 'up by adjacent coils, wires, tubes and other equipment and may even cause sparking to the extent of being a rire hazard between the parts of metallic or similar machinery and equipment which is non-electrical in nature. To reduce the loss 0i" wave energy from the guide joint, a wave trap is provided on the outer sides of the smaller guide member opposite to the inner surfaces at which the electric lines of force terminate.

This wave trap consists, mechanically 'sneaku ing, of a thin shim 5 whichV may consist of a good thick layer of solder or brazing material to which a plate 6 is braced or soldered so that the inner guide 3, the shim and the plate 6 form a solid structure. A portion of the wall of guide il is cut away to form a space which may be iilled with dielectric material such as polystyrene l. However, the space occupied by the polystyrene may be left empty of anything except air a1- though in such case the space would need to be longer because the velocity of transmission of electric waves through polystyrene is higher than through air. Any other well recognized dielectric having the properties of polystyrene may be used in place of the element These elements 5, S and 'I are duplicated on the opposite side of the inner wave guide. The closed end 'Ia of the space occupied by the element l comprises a short circuit and is located a half wavelength from the end of the smaller or inner guide. Approximately halfway between the surface 'la and the end of the inner guide there is an opening il into the space occupied by the element 'I and this opening is located approximately a quarter Wavelength from the end of the wave guide. With this structure it has been found that the wave energy leaking out or traversing the space between the inner and outer guides is greatly reduced. It has not been found necessary to locate any similar trapping means on the other two faces of the guides because the electric intensity falls off as this space is approached and is of very low or negligible value at the extreme sides. It has been found, however, in the case of high power equipment, that destructive or undesirable sparking tends to occur between the corner of plate G and the adjacent portions of the guide member 3. To prevent this, very small conductive plates 9 are connected conductively across between an edge of the plate B at its corner and the main body of the guide member 3.

Located beyond the plate 6 and away from the end of the guide, two pieces I5 of insulating material, which preferably may consist of material known as Bakelite, are rigidly attached to the inner guide by being mounted in bent-over flanges II of a thin metallic plate I2 which is soldered, brazed or otherwise rigidly attached to the main body of the guide member 3. At the top and bottom of these flanges additional bent-over members I3 may be provided to form a more rm and secure structure as a result of welding, brazing or soldering the bent-over portions I3 to the main body of the guide 3. The thicker portions of the insulating material I@ form the side bearings of the principal frictional engagement between the inner and outer guide and the end surfaces of the insulating members I form the principal bearing surfaces between the narrower portion-s of the inner and outer guides.

In addition to forming bearing surfaces the members I0 perform another useful function in that they further reduce any wave energy which passes by the wave trap otherwise known as a wave choke consisting of members 6, 1, 8, previously described. This energy is largely dissipated in heat because the dielectric material used is highly dissipative for electromagnetic waves.

We have found that the joint as so far described is not very smooth electrically, by which is meant that power flow through the guide tends to suffer renections at the joint due to the change in wave guide size. Unless some means are taken to avoid such reiiections some of the power is reflected back and in one embodiment tends to produce a standing wave ratio of about 2.5 decibels in both the large guide and the small guide. In constructions wherein the length of the guide changes due to the use of a sliding joint of this type, such reflections are particularly undesirable because as the guide length changes the impedance measured from any particular point down the large guide towards the joint becomes variable as the guide members slide in and out of one another to change the effective 4 guide length. In order to greatly reduce this reflection of energy and reduce the standing wave ratio, -small plate members I5 are rrnly set into slots in the narrow sides of the inner guide member 3. These plate members I5 project into the guide a short distance and comprise an inductive iris. When located a suitable distance from the end of the guide and when mounted in the narrow side of the guide these plates constitute an inductive iris. The amount of projection of the plates I5 into the guide and the distance of the center of the plates from the end of the guide have been determined eX- perimentally. These are related to the thickness of the plates I5 measured longitudinally along the guide. In speaking of the distance of the plates from the end of the guide it is understood that this distance is a function of the mean wavelength which the guide is expected to transmit. With an iris structure of this kind it has been found that the wave reection is very largely cancelled or neutralized so that the standing wave ratio and impedance variations are considerably reduced. In fact, with such a structure the wave guide joint is quite smooth" from an electrical standpoint.

Results somewhat similar may be obtained by placing iris forming members in the sides, that is, the long sides of the inner guide, in which case they form what is known as a capacitative iris. For Various reasons it is considered that the inductive iris is more effective than the capacitative iris. Among other reasons, iris members set in the long sides of the guide approach each other relatively closely and in the case of a small guide, sparking or electrical breakdown at the iris may result.

Although illustrated as a longitudinally extensible or trombone type wave guide joint in a rectangular guide which supports waves of the TE1,o type, it is not considered that the principles of the invention are limited to rectangular guides or to waves of this type. These principles may be extended to the case of wave guides supporting or transmitting waves of other modes of both the TE type and the TM types in rectangular guides and also to waves of various types in guides of circular, elliptical or other crosssections.

Wave guides, according to this specification, are elongated tubular uniconductors for the transmission of electrical wave energy such as are discussed in chapter 14, pages 455 to 487 under the title Hollow wave guides or merely Wave guide in the book entitled Ultra-High Frequency Techniques by Brainerd, Koehler, Reich and Woodruff, 15th printing, December 1943, by D. Van Nostrand Company, Inc.

What is claimed is:

1. An electromagnetic wave trap comprising members arranged about a body of solid dielectric of parallelepipoidal form thin with respect to its length and breadth, the length of the trap being defined as the dimension parallel to the direction of wave transmission, comprising (a) a body of conductive material contacting one side of the body, (b) conductive material solidly abutting and bounding one end of the body, (c) conductive material contacting one side of the body opposite to (a) but leaving a narrow strip of the body of said dielectric exposed at one end thereof, the edges of the body of said dielectric being bounded and closed to some extent by conductive members solidly conductively connecting (a) and (c).

2. A trap according to claim 1,` wherein the conductive members are narrowl longitudinally and laterally and lie close to the exposed end of the body of said dielectric.

3. A telescopingly adjustable wave guide joint comprising a wave guide member of smaller cross-section fitting slidably into a wave guide member of larger cross-section for intertransfer of electrical energy from one guide member to the other and including an iris forming member attached to and projecting internally into the said one guide member at a point located a short distance from the end of the inner member, the inner guide member extending in a longitudinal direction indefinitely beyond the iris away from the said end.

4. In a Wave guide joint comprising an inner guide member and an outer guide member of which the inner guide member is smaller in crosssectional dimension and lits into the outer guide member with a sliding fit, insulating means comprising the sole physical bearing or contact means between said members, as an element of means for coupling said sections to form a composite guide, iris means comprising plates oppositely extending into and rigidly conductively attached to said inner member near to but somewhat removed from the end thereof.

5. An electromagnetic wave guide joint whereby the mechanical length of a Wave guide may be varied with a minimum change of transmission therethrough comprising an inner member and an outer member into which the inner member telescopingly lits, the inner member having trap means on its outer surface, said trap means including a chamber having its terminus toward the end of the inner member open, i. e. not closed by conductive material, and its terminus away from the end of the inner member closed, i. e. blocked with conductive material, said chamber being laterally thin and having its inner and outer larger surfaces bounded by conductive material, said chamber being filled with dielectric material, such material including inter alia, atmosphere, the chamber having its nearer end at @t+1/4) wavelength from the end of the guide and being longitudinally (ac-|- 1/4) wavelength in length, in combination with iris means inside the inner guide member near the end thereof, and highly insulating material affixed to at least one of said inner and outer members in a form with extended surface to form a bearing between said members consisting of said insulating material exclusive of conductive material-to-conductive material contact, x being zero or any integer and the wavelength being any wavelength to be transmitted within the guide Iwithin the limits of measurement.

6. A longitudinally adjustable joint for a wave guide consisting of an outer wave guide member, an inner wave guide member slidably fitting into said outer wave guide member, said inner Wave guide member being provided with electromagnetic wave traps each comprising members arranged about a parallelepipoidal space of thickness small with respect to its length and breadth, the length of each trap being defined as the dimension parallel to the direction of Wave transmission, each trap comprising (a) conductive material dening one side of the space, (b) conductive material solidly closing and defining one end of the space, and (c) conductive material denning a side of the space opposite to (a) but leaving an entrance gap at one end thereof, the edges of the space being bounded and closed to some extent by conductive members solidly conduc- 6 tively connecting (u) and (chsaid traps being arranged in image relation to each other on opposite outer faces of the guide near the end of the section in combination with iris means within the guide near the end of the section.

'7. A longitudinally adjustable joint for wave guides comprising an inner member and an outer member into the end of which the inner member is adapted to slidingly nt, the inner member lhaving on its external surface an electromagnetic Wave trap comprising members arranged about a parallelepipoidal space of thickness small with respect to its length and breadth, the length of the trap being defined as the dimension parallel to the direction of wave transmission, comprising (a) conductive material denning one side of the space, (b) conductive material solidly closing and denning one end of the space, and (c) conductive material defining a side of the space opposite to (c) but leaving an entrance gap at one end thereof, the edges of the space being bounded and closed to some extent by conductive members solidly conductively connecting (a) and (c), in which the said trap means is near an end of the inner member and whereinthere are iris means provided inside the inner member.

8. A longitudinally adjustable joint for Wave guides comprising an inner member and an outer member into the end of which the inner member is adapted to slidingly fit, the inner member having on its external surface an electromagnetic Wave trap comprising members arranged about a parallelepipcidal space of thickness small with respect to its length and breadth, the length of the trap being dened as the dimension parallel to the direction of wave transmission, comprising (a) conductive material defining one side of the space, (b) conductive material solidly closing and defining one end of the space, and (c) conductive material dening a side of the space opposite to (a) but leaving an entrance gap at one end thereof, the edges of the space being bounded and closed to some extent by conductive members solidly conductively connecting (a) and (c), in which there are two said trap means on opposite outer faces of the inner member, and in which iris means are provided attached to the inside of the inner member upon the sides of the member which are at angles to the sides upon which the trap means are located.

9. A longitudinally adjustable joint for Wave guides comprising an inner member and an outer member into the end of which the inner member is adapted to slidingly nt, the inner member having on its external surface an electromagnetic wave trap comprising members arranged about a parallelepipoidal space of thickness small with respect to its length and breadth, the length of the trap being defined as the dimension parallel to the direction of Wave transmission, comprising (a) conductive material defining one side of the space, (b) conductive material solidly closing and defining one end of the space, and (c) conductive material defining a side of the space opposite to (a) but leaving an entrance gap at one end thereof, the edges of the space being bounded and closed to some extent by conductive members solidly conductively connecting (a) and (c), in which the said trap means is near an end of the inner member and wherein there are iris means xedly mounted within the inner member at a point nearer the said end than the trap means.

10. A longitudinally adjustable joint for wave guides comprising an inner guide member and an outer guide member into the end of which the inner membe'ris adapted to slidingly t, the inner member having on its external surface an electromagnetic wave trap comprising material arranged about a parallelepipoidal space of thickness small with respect to its length and breadth, the length of the trap being defined as the dimension parallel to the direction of wave transmission, comprising (a) conductive material defining one side of the space, (b) conductive material solidly closing and dening one end of the space, and (c) conductive material dening a side of the space opposite to (a) but leaving an entrance gap at one end thereof, the edges of the space being bounded and closed to some extent by conductive material solidly conductively connecting (a) and (c), wherein the nearest part of the trap means to the end of the guide is (r4-V4) wavelength therefrom, and iris means consisting of plates relatively thin in a longitudinal direction extending across and partially obstructing the inner guide member and located within and at (z+1/a) wavelength from the end of the inner guide member, :1: being Zero or any integer, and the wavelength being the wavelength of a Wave for the transmission of which the wave guide Iioint is designed.

11. A telescopingly adjustable wave guide joint comprising a wave guide member of smaller cross-section tting slidably into a wave guide member of larger cross-section for intertransfer of electrical energy from one guide member to theother and including an iris forming member attached to and projecting internally into the said one guide member at a point located a short distance from the end of the inner member, the

inner guide member extending in a longitudinal direction indefinitely beyond the iris away from the said end, wherein at least one of the members has attached thereto guiding and bearing means of highly insulating material of sumcient length and width whereby the physical sliding contact between the member consists solely of contact between said insulating material bearing against other material.

ALFRED C. BECK.

HARALD T. FRIIS.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,921,117 Darbord Aug. 8, 1933 2,151,118 King Mar. 21, 1939 2,165,961 Cork July 11, 1939 2,396,044 Fox Mar. 5, 1946 2,400,777 -Okress May 2l, 1946 2,404,086 Okress July 16, 1946 2,407,318 Mieher Sept. 10, 1946 2,427,100 Kihn Sept. 9, 1947 2,433,368 Johnson Dec. 30, 1947 2,434,509 Okress Jan. 13, 1948 2,451,876 Salisbury Oct. 19, 1948 2,465,719 Fernsler Mar. 29, 1949 2,479,220 Early Aug. 16, 1949 2,489,131 Hegbar Nov. 22, 1949 2,514,544 Hansen July 11, 1950 2,543,721 Collard Feb. 27, 1951 2,544,842 Lawson Mar. 13, 1951 FOREIGN PATENTS Number Country Date 503,467 Great Britain Apr. 6, 1939 

